1. Field of the Invention
The invention relates to a multi-lamp driver and more particularly to a multi-lamp driver used in a LCD backlight module.
2. Description of the Related Art
Illumination control of a backlight module in a LCD panel is typically realized by adjusting current in each lamp simultaneously. However, due to lamp nature, maximum and minimum values of current in each lamp are limited, resulting in insufficient difference between maximum and minimum value of total lamp illumination. This leads to poor performance, or even failure to comply with TCO03 standards.
FIG. 1 is a schematic diagram of a conventional multi-lamp driver 100 driving a first lamp Lp1 and second lamp Lp2. The multi-lamp driver 100 comprises a power driver 102, a feedback circuit 106, and a control circuit 108. The power driver 102 comprises a driving circuit 104 and a transformer T1. The driving circuit 104 converts DC voltage Vin to AC voltage, provided to a primary coil of the transformer T1. A secondary coil of the transformer T1 is coupled to high voltage ends of the first lamp T1 and second lamp T2 to provide power to the first lamp T1 and second lamp T2. The feedback circuit 106 is coupled to low voltage ends of the two lamps to generate a feedback signal Sf to the control circuit 108. The control circuit 108 then controls the driving circuit 104 based on an illumination control signal Sb and the feedback signal Sf, such that the AC voltage produced by the driving circuit 104 provides the two lamps Lp1 and Lp2 with stable illumination.
FIG. 2 is a schematic diagram of another conventional multi-lamp driver 200, comprising a power driver 202, a controlling circuit 104, a feedback circuit 106, and a control circuit 108. Here, multi-lamp driver 200 comprises two transformers T1 and T2 with secondary coils coupled respectively to high voltage ends of lamps Lp1 and Lp2 through capacitors C1 and C2. Further, the feedback circuit 106 is coupled to the secondary coil of the transformer T2 rather than to the low voltage ends of lamps Lp1 and Lp2. All other aspects of multi-lamp driver 100 and 200 are the same. Similarly, the control circuit 108 controls the driving circuit 104 based on an illumination control signal Sb and a feedback signal Sf received from the feedback circuit 104, such that the AC voltage produced by the driving circuit 104 provides the two lamps Lp1 and Lp2 with stable illumination.
As shown in FIGS. 1 and 2, illumination in both the multi-lamp drivers 100 and 200 is controlled by changing the AC voltage generated by the control circuit 108 to control currents of the lamps Lp1 and Lp2. During illumination adjustment, current in lamps Lp1 and Lp2 varies in the same manner and lamps Lp1 and Lp2 are turned on and off simultaneously. However, maximum and minimum current in the lamps Lp1 and Lp2 is limited, resulting in unobvious difference between maximum and minimum total lamp illumination of a panel. In view of such a problem, a multi-lamp driver with increased illumination range is called for.